EARLY RESPONSE OF SECOND—ROTATION <em>PINUS</em> <em>PATULA</em> STANDS TO NITROGEN AND PHOSPHATE FERTILIZERS AT SAO HILL FOREST PLANTATION, TANZANIA

Abstract

An investigation into the effect of fertilization on second-rotation Pinus patula stands as an option for increasing growth and yield was initiated in April 1998 at two sites in the Sao Hill forest plantation, Iringa region, southwest Tanzania. Six factorial fertilizer treatments consisting of nitrogen (N) (0, 60 kg N ha^-1) and phosphorus (P) (0, 30, 60 kg P ha^-1) were assigned randomly to one-year-old P. patula seedlings in April 1999. Tree heights were measured at 7, 18, 22, 30 and 42 months after out-planting. Diameter at breast height (dbh) was measured from 22 months onwards. At 7 months, seedlings were significantly taller at Ngwazi (0.45 ± 0.03 m) than at Msiwasi (0.36 ± 0.04 m). In contrast, although not significant, by 42 months trees were sligh tly taller at Msiwasi (5.00 ± 0.37 m) than at Ngwazi (4.87 ± 0.46 m) . Similarly, height increment measured at 42 months was significantly higher at Msiwasi. Msiwasi had significantly larger dbh trees ( 1.99 ± 0.36 cm) than Ngwazi (1.62 ± 0.0.30 cm)  at  22  months,  but these differences disappeared with time. Neither the application of N nor P had any effect on tree growth at Ngwazi. However, application of N depressed tree survival from 96 to 89% at Msiwasi. Application of P increased diameter and height growth at Msiwasi only. These results further stress the need for developing site-specific recommendations based on research studies.